I'm having this problem where i get very out of breath on playing long peices without rests. I get this feeling that I have too much air in my lungs and I get an urge to exhale. (Sort of like i'm not blowing out through the clarinet quick enough.)

My teacher is not quite sure why. I am making sure I play with plenty of diaphragm support, and that i don't breathe randomly. I'm not sure what the problem is. I'm wondering whether I might be taking too big breaths, or maybe it's something to do with getting anxious.